The purpose of the proposed research is to delineate factors, especially hormonal, that influence proliferation of peroxisomes and changes in peroxisome enzymes in liver, intestinal mucosa, kidney and adrenal cortex. Clofibrate (CPIB) and new hypolipidemic drugs without aryloxyisobutyrate structure will be used to stimulate peroxisome proliferation in desired tissues; endocrine ablative and supplementation regimes will be simultaneously maintained. Thereafter, electron cytochemical techniques and appropriate enzyme assays will be performed on tissues to give morphological and quantitative chemical data regarding peroxisome response. A second series of experiments involves exposure of rats to aflatoxin B1 during gestation alone, gestation plus suckling periods, suckling alone and post-weaning to study the effect of such differential exposure to a natural carcinogen on the incidence of hepatoma and other chronic liver injury.